1. Field of the Invention
The invention relates in general to a calibration mechanism mounted in a scanner, and more particularly to a scanner capable of scanning a transmissive document and a reflective document. The scanner may be a sheet-fed scanner, or a scan apparatus composed of an automatic document feeder and a flatbed scanner, and the scanner has two light sources.
2. Prior Art
Before scanning, a scanning module of a scanner first performs the white and dark shading correction. During the shading correction, a scan light source illuminates on a calibration sheet, which reflects light to the scanning module such that the white and dark shading correction and compensation can be performed. It is to be noted that if one of the scanning module and the calibration sheet can be moved relative to each other, the scanning module can obtain the reflected light corresponding to multiple scan lines, which is advantageous to the enhancement of the shading correction of the scanning module.
A typical document scanner, such as a sheet-fed scanner or a combination of a flatbed scanner and an automatic document feeder, generates an image signal corresponding to the document according to the reflected light from the surface of the document. In one configuration, the light source is installed on the chassis and the calibration sheet is disposed opposite the light source. When the scanning module is performing the calibration, the light source illuminates on the calibration sheet and the reflected light enters the scanning module.
When the above-mentioned scanner is used to scan a transmissive document, such as a film or a slide, the scanning light passes through the transmissive document and does not enter the scanning module.
One way to overcome this problem is to dispose a scanning module opposite the light source. Thus, the light passing through the transmissive document can enter the scanning module. However, since the calibration sheet has been disposed opposite the light source, the calibration sheet must be designed as a moveable device, or the light passing through the transmissive document would be obstructed by the calibration sheet. When the transmissive document is being scanned, the calibration sheet is moved to a suitable position without interfering with the path of the light passing through the transmissive document.
In addition to the above-mentioned design, the invention provides a calibration mechanism used in a scanner for scanning transmissive documents and reflective documents.